Many electronic devices require multi-functions and high-speed processing. Signals and radiation noises generated over printed circuit boards are factors that substantially degenerate performance of such electronic devices. In particular, electronic devices such as mobile phones and notebook computers with wireless communication functions are directly influenced by a noise failure. Thus, detecting a source of a noise and preventing a noise at a designing stage have been desired. As a measure against a noise, a structural designing evaluation utilizing an electromagnetic field simulation has been performed. However, a technique for measuring an electric field distribution at a surface and the proximity of an actual circuit board has not been established yet, and accuracy of the simulation has not been verified yet.
A technique is well known in which an antenna a size of which is approximately a wavelength of an electric field is used to measure an electric field distribution away from a printed circuit board. A measure has been considered in which an inverse operation is applied to an electric field distribution near a printed circuit board using a measurement result and design data of the printed circuit board to be measured. However, it is difficult to estimate an electric field radiated from each of wirings formed over a printed circuit board using the above described methods to measure an electric field distribution and applying the method to verify simulation accuracy is difficult.
Japanese Laid-open Patent Publication No. 2000-214200 discloses a neighboring magnetic field probe or a neighboring magnetic field probe system capable of detecting magnetic field component of an electromagnetic field caused near a circuit board with high spatial resolution. According to the Japanese Laid-open Patent Publication No. 2000-214200, a method for measuring a radiating magnetic field is employed in which an inductive current caused by a magnetic flux that transmits through a coil unit at a tip of a probe is detected. An electric field noise is blocked by providing a coil unit and a shield electrode along a transmission line and a magnetic field is detected with high resolution by making an area of a coil opening small.
Japanese Laid-open Patent Publication No. 2007-278820 discloses an electric field probe and an electric field measurement system capable of measuring an electric field component with high sensitivity. According to the Japanese Laid-open Patent Publication No. 2007-278820, an electric field is detected with a high sensitivity by exposing a core of a coaxial cable such as a semi-rigid cable, and covering the exposed core with a material having a high dielectric constant.
Japanese Laid-open Patent Publication No. H05-264672 discloses an electric field probe that enhances a shielding effect. According to the Japanese Laid-open Patent Publication No. H05-264672, unnecessary electric field components are shielded by narrowing a width of a dielectric layer disposed between an external conductor and an internal conductor of a coaxial cable.
Japanese Laid-open Patent Publication No. 2004-205416 discloses an electric field probe in which a tip end surface of a coaxial cable is sloped and a surface including a surface of the tip end of the coaxial cable is covered with a probe casing that is made up of an insulating material, and a tip of the internal conductor of the coaxial cable is exposed from the tip of the tip surface.
The magnetic field probe disclosed in Japanese Laid-open Patent Publication No. 2000-214200 provides a structure essentially for detecting a magnetic field, and a coil unit needs to be short-circuited in order to detect an electric field. Detecting an electric field using the short-circuited coil unit has a drawback in that electric field components coming from all direction are detected simultaneously at a transmission line of the exposed coil. In recent printed circuit boards, not only a width but only an interval of wirings have been miniaturized, thus the method disclosed in the Japanese Laid-open Patent Publication No. 2000-214200 detects electromagnetic field radiated from other wirings near a wiring to be measured or the surrounding elements. Hence, locating a source of an electric field noise in detail is difficult.
The electric field probe disclosed in the Japanese Laid-open Patent Publication No. 2007-278820 detects electric field components of all directions because the core is exposed. Thus, locating a source of an electric field noise in detail is difficult.
The electric field probe disclosed in the Japanese Laid-open Patent Publication No. H. 5-264672 has a limitation to make the dielectric layer thinner and unnecessary electric fields coming from the oblique directions are always detected when a section type electric probe is used as long as the dielectric layer exists. Hence, improving a spatial resolution has its limitation and locating a source of an electric field noise in detail is difficult.
Mostly an electric field radiated vertically from a wiring would need to be detected in order to locate a source of a noise radiated from a wiring in detail, in other words, electric field components radiated in parallel to a wiring needs to be shielded by an external conductor. However, the technique disclosed in the Japanese Laid-open Patent Publication No. H. 5-264672 detects, although slightly, an electric field coming from oblique directions. Mostly, vertical electric field components need to be extracted in order to achieve high spatial resolution. A probe structure that provides high spatial resolution lowers detection sensitivity, and the spatial resolution is degenerated when detection sensitivity is improved. Thus, switching probes are required for scanning a front surface of an object to be measured to identify a source of a noise, thus there is a drawback in that a measurement takes a long time. Sensitivity needs to be improved, for example, by filtering unnecessary frequencies when a frequency of a noise to be measured is known.
The electric field probe disclosed in the Japanese Laid-open Patent Publication No. 2004-205416 has a configuration in which the tip of the internal conductor of the coaxial cable is exposed from the surface. Therefore, as in the technique disclosed in Japanese Laid-open Patent Publication No. 2007-278820, electric filed components from all directions are detected and locating a source of a noise in detail is difficult.